1. Field of the Invention
The invention relates to a process for producing shaped sintered glass or sintered glass ceramic bodies and, more particularly, to a process for producing shaped sintered glass or sintered glass-ceramic bodies as high-strength construction and decoration materials simulating natural stone and used for cladding facades, walls and floors, both indoors and outdoors, that includes introducing a planar, uniformly thick layer of a mixture of broken glass, a mineral component and finely divided additives into a heat-resistant mold and drying it at a temperature of 60 to 100.degree. C.; heating the layer at a rate of at least 0.5 to 3.0 K/min to a sintering temperature; maintaining the sintering temperature for at least 20 minutes and then cooling the layer at a rate of at least 0.5 to 3.0 K/min to room temperature.
2. Prior Art
Numerous natural materials are employed for decorative applications both indoors and outdoors. Marble and granite are particularly widely used and are employed in large quantities for the internal and external cladding of prestige buildings. In addition to providing the decorative impression, it is also imperative that the corrosion resistance and economic production be assured. Naturally occurring materials do not always fulfil these demands, since it is often impossible to produce sufficiently large surfaces which have a uniform impression and since the corrosion resistance and strength are not always optimal, owing to the porosity of the natural material.
It is therefore known to replace the natural materials with artificially produced, glass-based shaped bodies which resemble natural stone and are in the form of panels.
For example, DE 41 25 698 C1 has disclosed a glass ceramic material having a composition (in % by weight, based on oxide) of
SiO.sub.2 64.1-72 Al.sub.2 O.sub.3 2.9-11 CaO 15.0-26 MgO 0-8 ZnO 0 .ltoreq. 2 BaO 0-0.5 K.sub.2 O 0-7.4 Na.sub.2 O 0-2 F 0.5-4
where .SIGMA. Na.sub.2 O, K.sub.2 O is at least 2, which material is used to replace natural stone for decorative applications and to cover floors and clad walls and facades in the construction industry.
Although glass ceramic offers an excellent decorative appearance as a replacement for natural stone, it is complex and expensive to produce, partly, for example, as a result of the complex process required to make it ceramic. Furthermore, relatively pure, and hence expensive, raw materials are required for its production.
Therefore, DE 43 19 808 C1 and DE 44 16 489 C1 have also disclosed the production of shaped bodies which resemble natural stone of the type mentioned above which are based on sintered glass or sintered glass ceramic. The starting material used for these sintering production processes is broken glass. The broken glass may be granulated glass made from flat glass and/or hollow ware, e.g. from bottles or containers, and mixtures thereof, with the possibility of also using some ecology cullet, recycled glass, e.g. from screen tubes, and glass remainders. Shaped sintered glass or sintered glass ceramic bodies produced from glass granules of this nature together with additives can therefore be produced cost-effectively and in an environmentally friendly manner.
For example, DE 43 19 808 C1 describes a process for producing high-strength construction and decoration materials which resemble natural stone, are in the form of panels and are used for cladding facades, walls and floors both indoors and outdoors, which materials comprise laminated individual layers of broken glass, additives, in particular sand, and mixtures thereof. In this known method, firstly a compressed stack of individual layers of the starting materials is built up in a heat-resistant mould, and this stack of layers is then subjected to a heat treatment which comprises a plurality of successive process steps.
Owing to the need to build up a multilayered stack and the resultant extensive heat treatment, producing the shaped bodies using this process is extremely complex.
By contrast, DE 44 16 489 C1 describes a less complex process for producing high-strength construction and decoration materials which resemble natural stone, are in the form of panels and are used for cladding facades, walls and floors both indoors and outdoors, in which the starting material comprises a mixture of broken glass, mineral components and finely divided additives, the mixture being produced from 85-98% by mass of broken glass, 0-14.7% by mass of a mineral component and a total of 0.3-5% by mass of finely divided additives. This mixture is then introduced, in a single planar, uniformly thick layer, into a heat-resistant mould, where it is dried at 60-110.degree. C. then heated at a rate of 0.5-3.0 K/min to 720-1100.degree. C., this temperature being held for 20-120 min. The layer is then cooled at a rate of 0.5-3.0 K/min to room temperature.
The abovementioned composition of the mixture and the temperature profile indicated ensure that the shaped bodies
do not react with the production mould PA1 there is no unevenness on the panel surface PA1 the panels are not deformed PA1 no bubbles, pores, inclusions and/or microcracks are formed in the top layer PA1 there is no need for any grinding and polishing work, and PA1 have a high tensile bending strength.
The advantages of the construction and decoration materials which are produced using the known process are that:
1. The tensile bending strength is at least 14-18 MPa, and if ZrO.sub.2 is used even reaches 19-23 MPa. PA0 2. There are no microcracks on the surface, so that a Class 1 speck resistance in accordance with DIN EN 122 is achieved. PA0 3. The appearance of different panels is more uniform and hence more reproducible than that of panels which are manufactured without the additives according to the invention and which, despite the manufacturing parameters being unchanged, often have entirely different appearances. PA0 4. The "elegant charm" of the panel surface is considerably more lifelike and strongly resembles specific types of natural stone, e.g. granite. PA0 5. The colours and structures of the material surfaces can be configured as desired. PA0 6. An independent, tasteful appearance is reproducible. PA0 7. The material has very few bubbles in the interior (otherwise, bubbles would have an adverse effect on any surface polishing). PA0 8. The use of recycled glass materials preserves stocks of natural stone and thus makes the above process ecologically advantageous as well.
The construction and decoration materials which resemble natural stone and are produced using the known process are highly durable and have a long service life. They are used for claddings for external and internal walls of structures produced in industrial, residential and traffic construction engineering, for furniture, work surfaces in kitchens and laboratories and for decorative works of art. The materials are distinguished by a high strength and hardness. The material is hygienic, easy to clean, withstands high temperatures, is chemically resistant, electrically nonconductive and is not combustible. The synthetic construction and decoration materials produced in this way are therefore better than natural, expensive materials, such as for example granite, marble or travertine.